Hey there, new problem with the 84 f150 4.9 inline 6.

This does this all the time now, when I am driving, whenever I let go of the gas and then when I press on the gas there is a defenite clunking sound as if metal hitting metal. Just once though until I depress and press again. Everytime I let go of the gas it clunks once.
It seems to be coming from right under the engine, or at least that is what it sounds like. Almost like the engine is surging forward and hitting something, but it seems to be coming from lower under the engine. Any takers?

Chris

 

Sounds like U-jonts. With the truck in neutral, engine off and emergency brake on, take a look at the driveshaft. Its a long tube connecting the engine/trans to the rear end. Sorry don't know your level of aquaintance. Anyways, grab it and turn, no lost motion is what is desired.

 

I went under and grabbed the shaft, (this sounds real dirt), and I could turn it left and right about 1/4 inch each way.

Chris

 

Agree with the possibility of u-joints. Need to look closely at the u-joint cross or tee movement as related to the end yokes. Should be absolutely no play.

Another possibility is a worn spline segment - where the output shaft of the tranny connects into the driveshaft.

Don't know that 1/4" movement is bad - all depends on where the free play is.

 

The whole driveshaft can turn either direction about 1/4 inch while the truck is parked in neutral.

 

4x4 or 2x4?

 

It is the 2x4 model, with a hydrolic clutch